This invention relates in general to electrical circuits, and more specifically to mixers.
Mixers take two input signals and multiply them together to realize a frequency translation. Standard Gilbert Cell based mixers require some amount of DC (direct current) bias current for nominal operation. This bias current results in an undesired power dissipation and limits low-power performance. This problem is exacerbated when bipolar topologies are utilized and input bias currents are required which dissipate additional quiescent power. Moreover, the bias current cannot simply be scaled down in order to achieve low-power operation. Scaling the currents affects the required loading conditions, frequency response, and gain performance. In extremely low-power/low-current applications, the required passive loads prove unmanageably large and active loads at high frequencies are not currently practical in the art. Gilbert Cell mixers also have a limited output voltage swing based on biasing and load conditions.
The undesired input bias currents associated with bipolar topologies can be eliminated by utilizing CMOS topologies but the unwanted DC bias tail current still remains. Another alternative is to use CMOS switching mixer topologies which solve the DC bias issues but they have high levels of carrier feedthrough due to charge injection and some don""t have the capability for rail-to-rail performance. A need thus exists in the art for a mixer circuit that can operate using no input or DC bias current and dissipates essentially no quiescent power while providing rail-to-rail output voltage swing.